diff --git a/config/config.exs b/config/config.exs
index 9cf6496..3540a88 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -18,6 +18,8 @@ config :parrhesia,
     max_event_bytes: 262_144,
     max_filters_per_req: 16,
     max_filter_limit: 500,
+    max_tags_per_event: 256,
+    max_tag_values_per_filter: 128,
     max_subscriptions_per_connection: 32,
     max_event_future_skew_seconds: 900,
     max_event_ingest_per_window: 120,
diff --git a/config/runtime.exs b/config/runtime.exs
index aafeca5..dbbf002 100644
--- a/config/runtime.exs
+++ b/config/runtime.exs
@@ -174,6 +174,16 @@ if config_env() == :prod do
         "PARRHESIA_LIMITS_MAX_FILTER_LIMIT",
         Keyword.get(limits_defaults, :max_filter_limit, 500)
       ),
+    max_tags_per_event:
+      int_env.(
+        "PARRHESIA_LIMITS_MAX_TAGS_PER_EVENT",
+        Keyword.get(limits_defaults, :max_tags_per_event, 256)
+      ),
+    max_tag_values_per_filter:
+      int_env.(
+        "PARRHESIA_LIMITS_MAX_TAG_VALUES_PER_FILTER",
+        Keyword.get(limits_defaults, :max_tag_values_per_filter, 128)
+      ),
     max_subscriptions_per_connection:
       int_env.(
         "PARRHESIA_LIMITS_MAX_SUBSCRIPTIONS_PER_CONNECTION",
diff --git a/lib/parrhesia/protocol/event_validator.ex b/lib/parrhesia/protocol/event_validator.ex
index 43942f8..de31e3c 100644
--- a/lib/parrhesia/protocol/event_validator.ex
+++ b/lib/parrhesia/protocol/event_validator.ex
@@ -6,6 +6,7 @@ defmodule Parrhesia.Protocol.EventValidator do
   @required_fields ~w[id pubkey created_at kind tags content sig]
   @max_kind 65_535
   @default_max_event_future_skew_seconds 900
+  @default_max_tags_per_event 256
   @supported_mls_ciphersuites MapSet.new(~w[0x0001 0x0002 0x0003 0x0004 0x0005 0x0006 0x0007])
   @required_mls_extensions MapSet.new(["0xf2ee", "0x000a"])
   @supported_keypackage_ref_sizes [32, 48, 64]
@@ -17,6 +18,7 @@ defmodule Parrhesia.Protocol.EventValidator do
           | :invalid_created_at
           | :created_at_too_far_in_future
           | :invalid_kind
+          | :too_many_tags
           | :invalid_tags
           | :invalid_content
           | :invalid_sig
@@ -87,6 +89,7 @@ defmodule Parrhesia.Protocol.EventValidator do
     created_at_too_far_in_future:
       "invalid: event creation date is too far off from the current time",
     invalid_kind: "invalid: kind must be an integer between 0 and 65535",
+    too_many_tags: "invalid: event tags exceed configured limit",
     invalid_tags: "invalid: tags must be an array of non-empty string arrays",
     invalid_content: "invalid: content must be a string",
     invalid_sig: "invalid: sig must be 64-byte lowercase hex",
@@ -169,16 +172,25 @@ defmodule Parrhesia.Protocol.EventValidator do
   defp validate_kind(kind) when is_integer(kind) and kind >= 0 and kind <= @max_kind, do: :ok
   defp validate_kind(_kind), do: {:error, :invalid_kind}
 
-  defp validate_tags(tags) when is_list(tags) do
-    if Enum.all?(tags, &valid_tag?/1) do
-      :ok
-    else
-      {:error, :invalid_tags}
-    end
-  end
+  defp validate_tags(tags) when is_list(tags), do: validate_tags(tags, max_tags_per_event(), 0)
 
   defp validate_tags(_tags), do: {:error, :invalid_tags}
 
+  defp validate_tags([], _max_tags, _count), do: :ok
+
+  defp validate_tags([tag | rest], max_tags, count) do
+    cond do
+      count + 1 > max_tags ->
+        {:error, :too_many_tags}
+
+      valid_tag?(tag) ->
+        validate_tags(rest, max_tags, count + 1)
+
+      true ->
+        {:error, :invalid_tags}
+    end
+  end
+
   defp validate_content(content) when is_binary(content), do: :ok
   defp validate_content(_content), do: {:error, :invalid_content}
 
@@ -510,4 +522,11 @@ defmodule Parrhesia.Protocol.EventValidator do
     |> Application.get_env(:limits, [])
     |> Keyword.get(:max_event_future_skew_seconds, @default_max_event_future_skew_seconds)
   end
+
+  defp max_tags_per_event do
+    case Application.get_env(:parrhesia, :limits, []) |> Keyword.get(:max_tags_per_event) do
+      value when is_integer(value) and value > 0 -> value
+      _other -> @default_max_tags_per_event
+    end
+  end
 end
diff --git a/lib/parrhesia/protocol/filter.ex b/lib/parrhesia/protocol/filter.ex
index fccdd4a..485158b 100644
--- a/lib/parrhesia/protocol/filter.ex
+++ b/lib/parrhesia/protocol/filter.ex
@@ -5,6 +5,7 @@ defmodule Parrhesia.Protocol.Filter do
 
   @max_kind 65_535
   @default_max_filters_per_req 16
+  @default_max_tag_values_per_filter 128
 
   @type validation_error ::
           :invalid_filters
@@ -19,6 +20,7 @@ defmodule Parrhesia.Protocol.Filter do
           | :invalid_until
           | :invalid_limit
           | :invalid_search
+          | :too_many_tag_values
           | :invalid_tag_filter
 
   @allowed_keys MapSet.new(["ids", "authors", "kinds", "since", "until", "limit", "search"])
@@ -36,6 +38,7 @@ defmodule Parrhesia.Protocol.Filter do
     invalid_until: "invalid: until must be a non-negative integer",
     invalid_limit: "invalid: limit must be a positive integer",
     invalid_search: "invalid: search must be a non-empty string",
+    too_many_tag_values: "invalid: tag filters exceed configured value limit",
     invalid_tag_filter:
       "invalid: tag filters must use #<single-letter> with non-empty string arrays"
   }
@@ -178,19 +181,33 @@ defmodule Parrhesia.Protocol.Filter do
     filter
     |> Enum.filter(fn {key, _value} -> valid_tag_filter_key?(key) end)
     |> Enum.reduce_while(:ok, fn {_key, values}, :ok ->
-      if valid_tag_filter_values?(values) do
-        {:cont, :ok}
-      else
-        {:halt, {:error, :invalid_tag_filter}}
+      case validate_tag_filter_values(values) do
+        :ok -> {:cont, :ok}
+        {:error, reason} -> {:halt, {:error, reason}}
       end
     end)
   end
 
-  defp valid_tag_filter_values?(values) when is_list(values) do
-    values != [] and Enum.all?(values, &is_binary/1)
-  end
+  defp validate_tag_filter_values(values) when is_list(values),
+    do: validate_tag_filter_values(values, max_tag_values_per_filter(), 0)
 
-  defp valid_tag_filter_values?(_values), do: false
+  defp validate_tag_filter_values(_values), do: {:error, :invalid_tag_filter}
+
+  defp validate_tag_filter_values([], _max_values, 0), do: {:error, :invalid_tag_filter}
+  defp validate_tag_filter_values([], _max_values, _count), do: :ok
+
+  defp validate_tag_filter_values([value | rest], max_values, count) do
+    cond do
+      count + 1 > max_values ->
+        {:error, :too_many_tag_values}
+
+      is_binary(value) ->
+        validate_tag_filter_values(rest, max_values, count + 1)
+
+      true ->
+        {:error, :invalid_tag_filter}
+    end
+  end
 
   defp filter_predicates(event, filter) do
     [
@@ -278,4 +295,12 @@ defmodule Parrhesia.Protocol.Filter do
     |> Application.get_env(:limits, [])
     |> Keyword.get(:max_filters_per_req, @default_max_filters_per_req)
   end
+
+  defp max_tag_values_per_filter do
+    case Application.get_env(:parrhesia, :limits, [])
+         |> Keyword.get(:max_tag_values_per_filter) do
+      value when is_integer(value) and value > 0 -> value
+      _other -> @default_max_tag_values_per_filter
+    end
+  end
 end
diff --git a/lib/parrhesia/web/connection.ex b/lib/parrhesia/web/connection.ex
index 0e814fa..586ba05 100644
--- a/lib/parrhesia/web/connection.ex
+++ b/lib/parrhesia/web/connection.ex
@@ -414,6 +414,7 @@ defmodule Parrhesia.Web.Connection do
                    :invalid_until,
                    :invalid_limit,
                    :invalid_search,
+                   :too_many_tag_values,
                    :invalid_tag_filter
                  ] ->
               Filter.error_message(reason)
@@ -462,6 +463,27 @@ defmodule Parrhesia.Web.Connection do
     restricted_count_notice(state, subscription_id, EventPolicy.error_message(reason))
   end
 
+  defp handle_count_error(state, subscription_id, reason)
+       when reason in [
+              :invalid_filters,
+              :empty_filters,
+              :too_many_filters,
+              :invalid_filter,
+              :invalid_filter_key,
+              :invalid_ids,
+              :invalid_authors,
+              :invalid_kinds,
+              :invalid_since,
+              :invalid_until,
+              :invalid_limit,
+              :invalid_search,
+              :too_many_tag_values,
+              :invalid_tag_filter
+            ] do
+    response = Protocol.encode_relay({:closed, subscription_id, Filter.error_message(reason)})
+    {:push, {:text, response}, state}
+  end
+
   defp handle_count_error(state, subscription_id, reason) do
     response = Protocol.encode_relay({:closed, subscription_id, inspect(reason)})
     {:push, {:text, response}, state}
@@ -648,6 +670,7 @@ defmodule Parrhesia.Web.Connection do
               :invalid_until,
               :invalid_limit,
               :invalid_search,
+              :too_many_tag_values,
               :invalid_tag_filter,
               :auth_required,
               :pubkey_not_allowed,
@@ -701,6 +724,7 @@ defmodule Parrhesia.Web.Connection do
               :invalid_until,
               :invalid_limit,
               :invalid_search,
+              :too_many_tag_values,
               :invalid_tag_filter
             ],
        do: Filter.error_message(reason)
diff --git a/test/parrhesia/config_test.exs b/test/parrhesia/config_test.exs
index 5de8a7a..2d160d0 100644
--- a/test/parrhesia/config_test.exs
+++ b/test/parrhesia/config_test.exs
@@ -6,6 +6,8 @@ defmodule Parrhesia.ConfigTest do
     assert Parrhesia.Config.get([:limits, :max_event_bytes]) == 262_144
     assert Parrhesia.Config.get([:limits, :max_event_future_skew_seconds]) == 900
     assert Parrhesia.Config.get([:limits, :max_event_ingest_per_window]) == 120
+    assert Parrhesia.Config.get([:limits, :max_tags_per_event]) == 256
+    assert Parrhesia.Config.get([:limits, :max_tag_values_per_filter]) == 128
     assert Parrhesia.Config.get([:limits, :event_ingest_window_seconds]) == 1
     assert Parrhesia.Config.get([:limits, :auth_max_age_seconds]) == 600
     assert Parrhesia.Config.get([:limits, :max_outbound_queue]) == 256
diff --git a/test/parrhesia/protocol/event_validator_marmot_test.exs b/test/parrhesia/protocol/event_validator_marmot_test.exs
index ffbf81e..fea4697 100644
--- a/test/parrhesia/protocol/event_validator_marmot_test.exs
+++ b/test/parrhesia/protocol/event_validator_marmot_test.exs
@@ -140,6 +140,18 @@ defmodule Parrhesia.Protocol.EventValidatorMarmotTest do
              EventValidator.validate(invalid_empty_content)
   end
 
+  test "rejects events with too many tags" do
+    event =
+      valid_keypackage_event(%{
+        "tags" => Enum.map(1..257, fn index -> ["e", "ref-#{index}"] end)
+      })
+
+    assert {:error, :too_many_tags} = EventValidator.validate(event)
+
+    assert {:error, "invalid: event tags exceed configured limit"} =
+             Protocol.validate_event(event)
+  end
+
   defp valid_keypackage_event(overrides \\ %{}) do
     base_event = %{
       "pubkey" => String.duplicate("1", 64),
diff --git a/test/parrhesia/protocol/filter_test.exs b/test/parrhesia/protocol/filter_test.exs
index 500e65c..95e7c72 100644
--- a/test/parrhesia/protocol/filter_test.exs
+++ b/test/parrhesia/protocol/filter_test.exs
@@ -40,6 +40,15 @@ defmodule Parrhesia.Protocol.FilterTest do
     assert {:error, :invalid_search} = Filter.validate_filters([%{"search" => ""}])
   end
 
+  test "rejects tag filters with too many values" do
+    filter = %{"#e" => Enum.map(1..129, &"event-ref-#{&1}")}
+
+    assert {:error, :too_many_tag_values} = Filter.validate_filters([filter])
+
+    assert Filter.error_message(:too_many_tag_values) ==
+             "invalid: tag filters exceed configured value limit"
+  end
+
   test "matches with AND semantics inside filter and OR across filters" do
     event = valid_event()
 
diff --git a/test/parrhesia/web/connection_test.exs b/test/parrhesia/web/connection_test.exs
index 2882618..0d5efc5 100644
--- a/test/parrhesia/web/connection_test.exs
+++ b/test/parrhesia/web/connection_test.exs
@@ -40,6 +40,38 @@ defmodule Parrhesia.Web.ConnectionTest do
     assert payload["approximate"] == false
   end
 
+  test "REQ rejects tag filters that exceed the configured value limit" do
+    state = connection_state()
+
+    payload =
+      JSON.encode!(["REQ", "sub-tag-limit", %{"#e" => Enum.map(1..129, &"ref-#{&1}")}])
+
+    assert {:push, {:text, response}, ^state} =
+             Connection.handle_in({payload, [opcode: :text]}, state)
+
+    assert JSON.decode!(response) == [
+             "CLOSED",
+             "sub-tag-limit",
+             "invalid: tag filters exceed configured value limit"
+           ]
+  end
+
+  test "COUNT rejects tag filters that exceed the configured value limit" do
+    state = connection_state()
+
+    payload =
+      JSON.encode!(["COUNT", "sub-tag-limit", %{"#e" => Enum.map(1..129, &"ref-#{&1}")}])
+
+    assert {:push, {:text, response}, ^state} =
+             Connection.handle_in({payload, [opcode: :text]}, state)
+
+    assert JSON.decode!(response) == [
+             "CLOSED",
+             "sub-tag-limit",
+             "invalid: tag filters exceed configured value limit"
+           ]
+  end
+
   test "AUTH accepts valid challenge event" do
     state = connection_state()